1. Field of the Invention
The present invention relates to a camera module package, and more particularly, to a camera module package that can prevent separation of a filter by strictly controlling the thickness of an adhesive by which the filter is adhered to a housing to reduce thermal stress at a region where the filter is adhered to the housing.
2. Description of the Related Art
In general, the current portable communication terminals, such as a cellular phone, a PDA (personal digital assistant), and a portable PC (personal computer), transmit image data as well as text or voice data and perform image communication.
According to such a trend, a camera module is basically installed at a mobile communication terminal in order to transmit the image data or perform the image communication.
FIG. 1 is a perspective longitudinal view illustrating a general camera module package 1. The camera module package 1 includes a lens barrel 10 having a lens 15 therein. A male thread 11 is formed on the outside of the lens barrel 10, and an incident hole 13 is formed through the center of a top surface of the lens barrel 10.
The lens barrel 10 is threadably engaged with a housing 20 that has a female thread 21 formed around the surface of an inner hole thereof. The housing 20 is provided with an IR-cut filter (hereinafter, referred to as a “filter”) 25 along the inner hole of the housing 20. The filter 25 blocks infrared rays included in light that passes through the lens 15.
A substrate 40 having an image sensor 30 mounted thereto is coupled to a lower end of the housing 20. The image sensor 30 has an image region where an image of an object passing trough the lens is formed.
The housing 20 has a protrusion 26 in order to include the filter 25 that removes infrared rays included in light so that the image sensor 30 can react to light like human eyes. The filter 25 is adhered and fixed to the protrusion 26 of the housing 20 by an adhesive 25a that is applied to an outer circumference of the filter 25 that corresponds to the protrusion 26.
However, in order to test durability and reliability of the camera module package 1 in which the filter 25 is adhered and fixed to the protrusion 26 of the housing 20, when a severe test is carried out for 120 hours under high temperature and humidity (humidity of 85% and temperature of 80° C.), the filter 25 is separated from the protrusion 26 of the housing 20.
The cause of the separation of the filter 25 will be described. As shown in FIG. 2, the housing 20 released from an injection mold is provided between a gate 3 and an overflow unit 4 of a runner hardening unit 2. The gate 3 and the overflow unit 4 are connected to longitudinal central regions of both left and right sides of the housing 20, respectively. Resin injected through the runner for injection molding of the housing 20 flows through the gate toward the overflow unit.
In this case, since air traps are formed in the housing 20 that corresponds to the gate 3 and the overflow unit 4, the entire surface height of the protrusion to which the filter is attached is not uniform but longitudinal central regions of individual sides have a larger surface height than both left and right regions thereof. Therefore, the thickness of the adhesive 25a applied to the longitudinal central region of the protrusion 26 becomes relatively smaller. This causes the separation of the filter in a region corresponding to the central region of the protrusion 26 of the housing 20.
Further, the housing 20, the filter 25, and the adhesive 25a have different thermal expansion coefficients from each other. Thermal stress is generated at a high temperature of 80° C. due to a difference in thermal expansion coefficient between the housing and the filter.
FIG. 3 is a distribution chart illustrating a result of thermal stress analysis of a housing, a filter, and an adhesive at a high temperature of 80° C. The adhesive 25a has a maximum thermal stress of 9.5 MPa at the corners thereof that correspond to the corners of the protrusion. When the thermal stress of the adhesive is relatively higher than adhesive strength of the adhesive, the separation of the filter is caused.